Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous and solid material, which include Nitrogen Oxides (NOx) and particulate matter. Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOx and particulates emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of NOx and particulate matter exhausted to the environment has been to recirculate exhaust gas from an engine back into the engine for subsequent combustion. The recirculated exhaust gas reduces the concentration of oxygen in the intake air supplied to the engine, which in turn lowers the maximum combustion temperature within cylinders of the engine. The reduced temperature decreases the formation of NOx. In addition, the exhaust gases contain some amount of particulate matter, which is burned upon recirculation through the engine cylinders, thereby lowering the amount of particulate matter exhausted to the environment.
When implementing exhaust gas recirculation (EGR), it may be necessary to tightly control the proportion of exhaust gas recirculated through the engine relative to fresh air drawn into the engine. For example, if the amount of exhaust gas recirculated through the engine is too great, the engine may not receive enough oxygen for proper operation and could possibly stall, produce insufficient levels of power, and/or produce excessive amounts of smoke and particulate matter because of poor combustion within the engine cylinders. Conversely, if the amount of exhaust gas recirculated into the engine is too little, the engine may not comply with NOx regulations.
Typically, the flow of exhaust gas back into the engine is regulated by way of a throttle arrangement in response to one or more input. The throttle arrangement generally includes a butterfly-type valve element disposed within an exhaust gas passageway and movable between open and closed positions to selectively pass or restrict the flow of exhaust gas to the intake of the engine. The valve element is moved between the open and closed positions based on a sensed mass flow rate of the exhaust. That is, a mass flow rate sensor is located within the exhaust gas passageway upstream or downstream of the throttle arrangement to generate a signal indicative of the flow rate of exhaust passing into the engine. A controller located elsewhere on the engine receives the exhaust flow rate signal, and generates a position command directed to a drive motor of the throttle arrangement.
One attempt at determining the flow rate and regulating the flow rate of air with a compact arrangement is described in U.S. Pat. No. 6,997,162 (the '162 patent), issued to Hirayama et al. on Feb. 14, 2006. Specifically, the '162 patent describes an electronically controlled throttle body having a main air passage and a valve element disposed therein. The valve element is driven by a motor, which is externally mounted to the throttle body in a generally perpendicular direction relative to the main air passage. The '162 patent also describes determining mass flow via a hot wire-type air flow meter, and a microcomputer integrated together with the main air passage, the valve element, and the motor to form a single body. The microcomputer receives signals from the flow meter indicative of the flow rate of fresh air entering the engine, calculates a pressure of the air based on the signals from the flow meter, and controls the drive motor to move the valve element based on the flow rate signals and calculated pressure.
Although the '162 patent may describe the regulation of an air flow rate into an internal combustion engine, it may still have a limited use. In particular, because the method receives the mass flow rate signal from a mass flow sensor, rather than determining the mass flow rate based on temperature and pressure, it may be more costly or require more computing power.
The disclosed method of determining EGR mass flow rate is directed to overcoming one or more of the problems set forth above.